Traditionally, electronic displays such as liquid crystal displays have been made by sandwiching an optoelectrically active material between two pieces of glass. In many cases each piece of glass has an etched, clear electrode structure formed using indium tin oxide. A first electrode structure controls all the segments of the display that may be addressed, that is, changed from one visual state to another. A second electrode, sometimes called a counter electrode, addresses all display segments as one large electrode, and is generally designed not to overlap any of the rear electrode wire connections that are not desired in the final image. Alternatively, the second electrode is also patterned to control specific segments of the display. In these displays, unaddressed areas of the display have a defined appearance.
Electrophoretic display media, generally characterized by the movement of particles through an applied electric field, are highly reflective, can be made bistable, and consume very little power. Encapsulated electrophoretic displays also enable the display to be printed. These properties allow encapsulated electrophoretic display media to be used in many applications for which traditional electronic displays are not suitable, such as flexible displays. The electro-optical properties of encapsulated displays allow, and in some cases require, novel schemes or configurations to be used to address the displays.
"Shutter mode" electrophoretic displays are configured so that the particles can switch between a largely light-blocking (or reflecting) state and a largely light-transmitting state. These displays often are constructed with particles which can migrate between a smaller and larger electrode. Migration of the particles to the large electrodes allows them to spread out, causing the capsule to take on the visual properties of the particles. Migration of the particles to the smaller electrode causes the capsule to take on the visual properties of the dispersing fluid or of the larger electrode, because the particles are "clumped" together near the smaller electrode. Another use of this effect is to control transmission of light through the capsule. The drawback to shutter mode displays is that the electrodes must be etched very precisely.